The present invention concerns printing apparatuses in general, for example, screen printing or graphic arts apparatuses, which may include printing apparatuses of the endless chain drive, rotary, or straight path varieties.
For purposes of illustration, screen printing apparatuses are largely discussed herein, although the present invention is applicable to various other types of printing devices.
The problems associated with proper alignment between a screen registered in a screen printing apparatus and the object to be printed, such as an article of clothing, are well known. These alignment problems become exacerbated over time and increase in complexity with increasing numbers of screens used to effectuate certain designs. For example, multicolor screen printing typically involves a plurality of screens, each screen being provided with a certain design or part of a design which has a particular color associated therewith. Proper registration of each screen is important especially when an object is printed with more than one color or design. Registration may be in the x-direction (e.g. left/right), y-direction (front/back), or theta-direction (rotation about a z-axis perpendicular to the x-y plane).
As generally used herein, registration refers to the placement of individual screens each containing a color which collectively comprise the entire design in a relationship to each other so that when each screen individually transfers its color image to the substrate, the colors making up the design are in an optimum relationship to each other.
With present devices, any registration adjustment to the screen will affect all phases of alignment to various degrees because existing machines generally attempt to correct deficiencies in the position of a screen by trying to correct each of the x, y and theta adjustments at one time. Thus, any adjustment made to correct misregistration affects the entire image and typically results in numerous subsequent adjustments, almost in an iterative manner. For example, an adjustment along the y axis may unintentionally produce a misalignment in the angular orientation of the screen, thereby requiring further adjustment to the theta registration. Conversely, adjustments about the theta axis invariably affect both y and x direction positions simultaneously, thereby requiring further adjustment. Similarly, adjustments to x-registration positions will affect the theta position, which also in turn affects the y position.